This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-374650, filed Dec. 7, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
This invention relates to a pressure-resistant balloon. More particularly, the invention relates to pressure-resistant balloons such as a scientific observation balloons used in stratosphere or a cosmic observation, recreational hot-air balloons, and gas balloons.
2. Description of the Related Art
Some scientific observation balloons are designed to fly in the stratosphere at altitudes ranging from 30 to 40 km. To regulate the flying altitude of such a high-altitude balloon, the buoyant gas is discharged from the balloon to reduce the buoyancy and certain amount of ballast is dropped to recover the high flying-altitude. However, the flying altitude can no longer be regulated once all ballast is dropped.
A super-pressure balloon having a pressure-resistant gasbag that withstands high internal pressures to stay at high flying-altitudes is known. The gasbag is inflated to its maximum capacity, and the buoyant gas is not discharged from the gasbag. Maintaining the maximum capacity and the internal gas pressure, the super-pressure balloon keeps rising. As the balloon rises, its buoyancy is reduced to a certain extent due to a decrease in air density. Eventually, the balloon assumes state of equilibrium at a certain altitude. Then, the balloon keeps flying in the horizontal direction at that altitude. If the internal gas temperature falls after sunset, the internal gas pressure decreases. Despite the decrease of the internal gas pressure, the gasbag can maintain its maximum volume. The super-pressure balloon can therefore continue to flying horizontally without the necessity of dropping ballast. Thus, the super-pressure balloon can fly for a long time, with no need to drop large amount of ballast, unlike the conventional balloons. Although the super-pressure balloon can maintain a certain altitude, it cannot change its flying altitude without difficulty.
Some super-pressure balloons have an air bag provided within the gasbag. Air is injected into the air bag, changing the effective volume of the gasbag in order to change the flying altitude of the balloon. In the stratosphere where air is very thin, however, a strong blower or a pump must be used to inflate the air bag within a short time. However, the use of a strong blower or pump is not feasible particularly in the case of a large size balloon.
A pressure-resistant balloon comprises an airtight pressure-resistant gasbag and a volume changing mechanism which deforms the gasbag in a fully inflated state to change a volume of the gasbag. The gasbag includes a plurality of spindle-shaped gores of an airtight film material, adjacent gores joined together at side edges, and a set of load tapes fitted to joined sections of the side edges, the load tapes extending along the side edges, respectively. The gasbag, after inflated, allows no gas to be discharged so as to maintain an internal gas pressure. Each of the gores outwardly protrudes between two adjacent load tapes extending along the side edges of the gore, respectively, without an elongation of the airtight film material of the gore, when the gasbag is in the fully inflated state. The protruding gore has a radius of curvature in a direction intersecting with the two adjacent load tapes. The radius of curvature is smaller than a radius of the gasbag. The protruding gore is subject to a tensile force which is directed in the direction intersecting with the two adjacent load tapes.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.